This invention relates to a fluorine-substituted 4-alkenylbenzoic acid and derivatives thereof, which are useful as electro-optical display materials, and a nematic liquid crystal composition containing cyanophenyl benzoate derivatives and a liquid crystal display system using the same.
TN-LCD (twisted nematic liquid crystal display device) is a typical liquid crystal display device and used in clocks, electronic calculators, electronic pocketbooks, pocket computers, word processors, personal computers and the like. On the other hand, with the increase in the information contents of OA instruments, STN (super twisted nematic)-LCD has been developed by Scheffer et al. (SID ""85 Digest, p. 120, 1985) and Kinugawa et al. (SID ""86 Digest, p. 122, 1986) and is now popularizing in the field of portable terminals, electronic pocketbooks, pocket computers, word processors, personal computers, monitor displays and the like high information displays.
Recently, an active addressing drive system (Proc. 12th IDC, p. 503, 1992) and multiline addressing drive system (SID ""92 Digest, p. 232, 1992) have been proposed for the purpose of improving response characteristics of STN-LCD. Also, with the aim of achieving brighter display or higher contrast ratio, a novel reflection type liquid crystal color display system in which birefringence of liquid crystal and retardation film was used in stead of color filter layers (The Institute of Television Engineers of Japan, Technical Reports, vol. 14, No. 10, p. 51, 1990) and a liquid crystal display device having a refracting surface in which a small parboloid is arranged on the substrate electrode side have been proposed.
Particularly, uniform and high contrast display against the temperature distribution of back light is expected for the purpose of enlarging the display area, so that liquid crystal materials having more stable orientation and smaller temperature-dependency are expected, and a birefringence corresponding to a predetermined value is also expected for reducing dispersion of cell thickness. Since high duty drive is carried out by increasing the number of pixels, response, gradient and the like are also regarded as important factors. In the case of medium and small size portable displays, on the other hand, stability of display against working environmental temperature is an important point, so that liquid crystal materials having lower driving voltage which can reduce response and consumptive electric power are expected, as well as smaller temperature dependency of driving voltage, sharpness and frequency-dependency of desired duty drive within the temperature range of from xe2x88x9230 to 0xc2x0 C. or from 40 to 80xc2x0 C. In addition, though it is necessary to avoid too low electrical resistance (specific resistance) for saving consumptive electric power, it is required to set the resistance to a predetermined value so that it does not become too high which will cause image sticking. Thus, liquid crystal materials which are differentiated further in detail and improved even to a certain degree are still in demand.
As has been described in detail in the foregoing, there are many demands for liquid crystal display devices, such as more precise and high density display capacity, quicker response speed (switching time) against driving voltage and environmental temperature, lower driving voltage having chemically and electrically high stability, higher gradient and higher contrast for working environmental temperature and viewing angle. Because of this, research and development are still carried out on liquid crystal materials which can achieve desired driving voltage, particularly lower driving voltage, with lower viscosity so that the response property can be improved while having the nematic property within a wide range of temperature and maintaining the nematic phase for a prolonged period of time under low temperature storage conditions. In addition, designing of birefringence, dielectric anisotropy and elastic constant and their temperature-dependency, light wave length-dependency of birefringence and frequency-dependency of dielectric anisotropy in response to duty numbers are also drawing attention as means to be improved.
To meet such demands for liquid crystal materials, it is necessary to generally optimize birefringence, elastic constant, dielectric anisotropy, lower viscosity, wider nematic temperature range, chemical stability, electric stability (desired specific resistance) and the like physical characteristics and predetermined tilt angle concerning orientation property, wider d/p margin and the like individual characteristics, and the development of new liquid crystal compounds or liquid crystal compositions is still in demand.
With regard to the compounds related to the groups A1 to A3 of the present invention, which will be described in the following, compounds of the general formula (I-1) are described for example in German Patent 2306739 (1973) and J. Phys. (Paris), Suppl. 36, C1, 387 (1975), compounds of the general formula (I-4) are described in JP-A-58-83665 (1983) (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) and U.S. Pat. No. 4,455,261 (1984) and compounds of the general formulae (I-2), (I-3) and (I-5) to (I-9) are described in JP-W-3-503637 (the term xe2x80x9cJP-Wxe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese international patent applicationxe2x80x9d) and WO 89/08102 (1989). Compositions in which these compounds are used are described for example in JP-A-9-157654 (1997) in addition to the just described references.
With regard to compounds related to the groups A4 to A6 of the present invention, which will be described in the following, compounds of the general formulae (I-10) and (I-13) are described in JP-A-2-225444 (1990), JP-A-2-233656(1990), European Patent 464648 (1991), European Patent 466183 (1991) and JP-A-4-230352 (1992), and compounds of the general formula (I-16) are described for example in JP-A-4-300861 (1992).
In addition to the aforementioned references, compositions in which these compounds are used are described for example in JP-W-62-501509 (1986), U.S. Pat. No. 4,818,426 (1989), European Patent 207975 B (1990), JP-W-63-5025969 (1987), JP-W-1-500837 (1988), JP-A-4-279560 (1992), WO 96/32365 (1996), JP-A-9-59625 (1997), JP-A-9-227866 (1997), JP-A-10-88140. (1998), JP-A-10-140157 (1998) and JP-A-10-158651 (1998).
However, the aforementioned techniques, even some of them are unrealized, are not sufficient for achieving objects of the present invention. For example, compounds of the general formulae (I-11) and (I-12) and compounds of the general formulae (I-14) and (I-15) or the general formulae (I-17) and (I-18) of the present invention are not known. With regard to techniques concerning the compositions, descriptions about general combinations of compounds can be found illustratively, but their illustrative examples are rare, so that technical disclosures which can be used easily by those skilled in the art are not sufficient yet.
In addition, even if the aforementioned techniques are used, problems still remain unsettled. For example, great concern has been directed toward the improvement of the response property of liquid crystal display by smaller viscoelasticity in comparison with the size of dielectric anisotropy xcex94∈ or the realization of liquid crystal display which can be driven within a wide range of temperature by obtaining a nematic phase that is stable at a low temperature through the reduction of a crystallizing or precipitating tendency against other liquid crystal materials. Also, in the case of word processors, personal computers and the like STN-LCDs having large information capacity, small frequency dependency of driving voltage to cope with high duty, or small temperature dependency of driving voltage in the case of portable use, is expected. Because of this, more excellent new liquid crystal materials are expected.
This invention contemplates overcoming the aforementioned problems involved in the prior art.
Illustratively, its primary object is to provide a novel liquid crystal compound which is strong polar compound having large dielectric anisotropy and exerts excellent threshold voltage reducing effect and excellent miscibility with conventional liquid crystal materials by its addition.
Another object of the present invention is to provide liquid crystal materials in response to each purpose without spoiling other characteristics, including a case of its addition in a small amount. More particularly, the object is to expand operating temperature range of liquid crystal display characteristics through the improvement of miscibility, low temperature shelf life and the like, to improve reduction of driving voltage and its temperature changes and to achieve or improve relatively quick response to a desired driving voltage.
Still another object is to provide TN-LCD, STN-LCD and the like liquid crystal display systems with improved electro-optical characteristics making use of the liquid crystal compositions as constituting materials.
The present invention have found the following items as means for overcoming the aforementioned problems:
1. a compound, represented by the general formula (I): 
wherein R represents a hydrogen atom or a straight chain alkyl group having 1 to 7 carbon atoms and each of X, Y and Z independently represents hydrogen atom or fluorine atom.
2. The compound described in the aforementioned item 1, wherein R is a hydrogen atom or a methyl group.
3. The compound described in the aforementioned item 1 or 2, wherein X is a fluorine atom and Y is a hydrogen atom.
4. A compound, represented by the general formula (II): 
wherein R represents a hydrogen atom or a straight chain alkyl group having 1 to 7 carbon atoms and Z represents a hydrogen atom or a fluorine atom.
5. A nematic liquid crystal composition, comprising:
a liquid crystal component A composed of 1, 2 or 3 or more groups selected from groups A1 to A6, wherein said groups are composed of compounds represented by the general formulae (I-1) to (I-18): 
wherein R11 each independently represents an alkyl or alkoxy group having 1 to 10 carbon atoms and R12 each independently represents an alkenyl or alkenyloxy group having 2 to 10 carbon atoms, wherein said alkyl group, alkoxygroup, alkenyl group or alkenyloxy group may be unsubstituted or may have one F, CH3 or CF3 as a substituent group, and/or at least one of CH2 groups existing in said alkyl group, alkoxy group, alkenyl group or alkenyloxy group may be substituted each independently with xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94 or xe2x80x94COOxe2x80x94 where O atoms are not directly linked to each other, and the atoms which constitute these compounds may be replaced by their isotopes, and
said liquid crystal component A is composed of 1 to 20 compounds;
0 to 95% by weight of a liquid crystal component B composed of compounds having a dielectric anisotropy of +2 or more; and
0 to 95% by weight of a liquid crystal component C composed of compounds having a dielectric anisotropy of from xe2x88x9210 or more to less than +2;
wherein the total amount of the liquid crystal component B and liquid crystal component C in said nematic liquid crystal composition is from 30 to 90% by weight, with the proviso that the liquid crystal component A should satisfy at least one of the following conditions (i) to (viii):
(i) said liquid crystal component A contains at least one compound selected from the compounds represented by said general formulae (I-11), (I-12), (I-14), (I-15), (I-17) and (I-18), and the content of said compound in said liquid crystal component A is from 5 to 100% by weight;
(ii) said liquid crystal component A contains 1 to 10 of the compounds represented by the group A5 and 1 to 10 of the compounds represented by the group A4 and/or group A6, and the total content of these compounds in said liquid crystal component A is from 5 to 100% by weight;
(iii) said liquid crystal component A contains 1 to 10 of the compounds represented by the group A6 and 1 to 10 of the compounds represented by the group A4 and/or group A5, and the total content of these compounds in said liquid crystal component A is from 5 to 100% by weight;
(iv) said liquid crystal component A contains 1 to 10 of the compounds represented by the groups A4 to A6 in which the side chain group has an alkenyl group and 1 to 10 of the compounds represented by the groups A1 to A3 in which the side chain group has an alkyl group, and the total content of these compounds in said liquid crystal component A is from 5 to 100% by weight;
(v) said liquid crystal component A contains 1 to 10 of the compounds represented by the group A3 and/or group A6 having 3,5-difluoro-4-cyanophenyl group and 1 to 10 of the compounds represented by the group A2 and/or group A5 having 3-fluoro-4-cyanophenyl group, wherein at least one of these selected compounds belongs to the group A5 or group A6, and the total content of these compounds in said liquid crystal component A is from 5 to 100% by weight;
(vi) said liquid crystal component A contains 1 to 10 of the compounds represented by the group A3 and/or group A6 having 3,5-difluoro-4-cyanophenyl group and 1 to 10 of the compounds represented by the group A1 and/or group A4 having 4-cyanophenyl group, wherein at least one of these selected compounds belongs to the group A4 or group A6, and the total content of these compounds in said liquid crystal component A is from 5 to 100% by weight;
(vii) said liquid crystal component A contains 1 to 10 of the compounds represented by the group A3 and/or group A6 having 3,5-difluoro-4-cyanophenyl group, 1 to 10 of the compounds represented by the group A2 and/or group A5 having 3-fluoro-4-cyanophenyl group and 1 to 10 of the compounds represented by the group A1 and/or group A4 having 4-cyanophenyl group, and the total content of these compounds in said liquid crystal component A is from 5 to 100% by weight; and
(viii) said liquid crystal component A contains 1 to 10 of compounds in which R12 is represented by CH2xe2x95x90CHxe2x80x94, CH2xe2x95x90CHxe2x80x94(CH2)2xe2x80x94, CH2xe2x95x90CHxe2x80x94(CH2)4xe2x80x94, CH3CHxe2x95x90CHxe2x80x94, CH3CHxe2x95x90CHxe2x80x94(CH2)2xe2x80x94 or CH3CHxe2x95x90CHxe2x80x94(CH2)4.
6. The nematic liquid crystal composition described in the aforementioned item 5, wherein said liquid crystal component B contains 1 to 15 compounds selected from the group of compounds represented by the general formulae (II-1) to (II-4): 
wherein each of R21 to R24 independently represents an alkyl group having 1 to 10 carbon atoms or an alkenyl group having 2 to 10 carbon atoms, wherein said alkyl group or alkenyl group may be unsubstituted or may have one F, CH3 or CF3 as a substituent group, and/or at least one of CH2 groups existing in said alkyl group or alkenyl group may be substituted each independently with xe2x80x94Oxe2x80x94, xe2x80x94COxe2x80x94 or xe2x80x94COOxe2x80x94 where O atoms are not directly linked to each other, each of X21 to X24 independently represents F, Cl, CF3, OCF3, OCF2H, NCS or CN, each of Y21 to Y28 independently represents H, F, Cl or OCF3, each of W21 to W29 independently represents H, F or Cl, each of Z21 to Z26 independently represents a single bond, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Nxe2x95x90CHxe2x80x94 or xe2x80x94N(O)xe2x95x90Nxe2x80x94, wherein each of Z21 and Z24 to Z26 may be xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, each of the rings A21 to A24 independently represents trans-1,4-cyclohexylene, trans-1,4-cyclohexenylene or trans-1,3-dioxane-2,5-diyl, wherein the ring A24 may be 1,4-phenylene, 2- or 3-fluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and in the case of trans-1,4-cyclohexylene, at least one of the hydrogen atoms in said ring may be replaced by deuterium atom, each of k21 to k24 independently represents 0 or 1 wherein k23+k24 is 0 or 1, and the atoms which constitute the compounds of said general formulae (II-1) to (II-4) may be replaced by their isotopic atoms.
7. The nematic liquid crystal composition described in the aforementioned item 6, wherein said liquid crystal component B contains 1 to 15 or more compounds selected from the group consisting of (1) a compound in which each of R21 to R24 in the general formulae (II-1) to (II-4) is independently an alkenyl group having 2 to 5 carbon atoms, (2) a compound in which each of X21 to X24 in the general formulae (II-1) to (II-4) is independently F, Cl, or OCF3, (3) a compound in which Z22 in the general formula (II-1) is xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2)4xe2x80x94, (4) a compound in which k21 in the general formula (II-1) is 1, (5) a compound in which at least one of Y23, Y24, W21 and W22 in the general formula (II-2) is F, (6) a compound in which in the general formula (II-2) k22 is 1 and Z24 is xe2x80x94Cxe2x89xa1Cxe2x80x94, (7) a compound in which in the general formula (II-2) Z23 is a single bond or xe2x80x94(CH2)2xe2x80x94 and Z24 is xe2x80x94COOxe2x80x94, (8) a compound in which at least one of Y25, Y26 and W23 to W26 in the general formula (II-3) is F, (9) a compound in which Z26 in the general formula (II-3) is xe2x80x94Cxe2x89xa1Cxe2x80x94, (10) a compound in which in the general formula (II-3) Z25 is a single bond or xe2x80x94Cxe2x89xa1Cxe2x80x94 and Z26 is xe2x80x94COOxe2x80x94, (11) a compound represented by the general formula (II-4), and (12) a compound in which in the general formulae (II-1) and (II-2) the rings A21 to A23 are trans-1,4-cyclohexylene and at least one of the hydrogen atoms in said ring is replaced by deuterium atom.
8. The nematic liquid crystal composition described in the aforementioned item 6, wherein said liquid crystal component B contains 1 to 15 compounds selected from the group consisting of (1) a compound in which in the general formula (II-1) R21 is an alkyl or alkenyl group having 2 to 5 carbon atoms, k21 is 0 and X21 is xe2x80x94CN, (2) a compound in which in the general formula (II-1) k21 is 1, X21 is F or xe2x80x94CN and each of Y21 and Y22 is independently H or F, (3) a compound in which in the general formula (II-2) R22 is an alkyl or alkenyl group having 2 to 5 carbon atoms, k22 is 0, X22 is xe2x80x94CN and each of Y23, Y24, W21 and W22 is independently H or F, (4) a compound in which in the general formula (II-2) k22 is 1, Z23 is a single bond, xe2x80x94(CH2)2xe2x80x94 or xe2x80x94COOxe2x80x94, Z24 is a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, X22 is F or xe2x80x94CN and each of Y23, Y24, W21 and W22 is independently H or F, (5) a compound in which in the general formula (II-3) R23 is an alkyl or alkenyl group having 2 to 5 carbon atoms and one of Z25 and Z26 is a single bond and the other is a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, (6) a compound in which each of Y25, Y26 and W23 to W26 in the general formula (II-3) is H or F, (7) a compound in which in the general formula (II-4) R24 is an alkyl or alkenyl group having 2 to 7 carbon atoms and k23+k24 is 0, and (8) a compound in which in the general formulae (II-1) and (II-2) the rings A21 to A23 are trans-1,4-cyclohexylene and at least one of the hydrogen atoms in said ring is replaced by deuterium atom; and
wherein the total content of these compounds in said liquid crystal component B is from 10 to 100% by weight.
9. The nematic liquid crystal composition described in the aforementioned item 6, wherein said liquid crystal component B contains 1 to 15 compounds selected from the group consisting of (1) a compound in which in the general formula (II-1) R21 is an alkyl or alkenyl group having 2 to 5 carbon atoms, k21 is 1, one of Z21 and Z22 is a single bond and the other is a single bond, xe2x80x94COOxe2x80x94, xe2x80x94(CH2)2xe2x80x94 or xe2x80x94(CH2)4xe2x80x94, X21 is F, Cl, CF3, OCF3 or OCF2H and at least one of Y21 and Y22 is F, (2) a compound in which in the general formula (II-2) R22 is an alkyl or alkenyl group having 2 to 5 carbon atoms, k22 is 1, Z23 is a single bond, xe2x80x94(CH2)2xe2x80x94 or xe2x80x94COOxe2x80x94, Z24 is a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, X22 is F, Cl, CF3, OCF3 or OCF2H, at least one of Y23 and Y24 is F and each of W21 and W22 is independently H or F, (3) a compound in which in the general formula (II-3) R23 is an alkyl or alkenyl group having 2 to 5 carbon atoms, one of Z25 and Z26 is a single bond and the other is a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, X23 is F, at least one of Y25 and Y26 is F and W23 to W26 are H or one or more of them are F, and (4) a compound in which in the general formulae (II-1) and (II-2) the rings A21 to A23 are trans-1,4-cyclohexylene and at least one of the hydrogen atoms in said ring is replaced by deuterium atom; and
wherein the total content of these compounds in said liquid crystal component B is from 10 to 100% by weight.
10. The nematic liquid crystal composition described in any one of the aforementioned items 5 to 9, wherein said liquid crystal component C contains 1 to 15 compounds selected from the group consisting of compounds represented by the general formulae (III-1) to (III-4): 
wherein each of R31 to R34 independently represents an alkyl or alkoxy group having 1 to 7 carbon atoms or an alkenyl or alkenyloxy group having 2 to 7 carbon atoms, wherein said alkyl group, alkoxy group, alkenyl group or alkenyloxy group may be unsubstituted or may have one F, CH3 or CF3 as a substituent group, and/or at least one of CH2 groups existing in said alkyl group, alkoxy group, alkenyl group or alkenyloxy group may be substituted each independently with xe2x80x94Cxe2x80x94, xe2x80x94COxe2x80x94 or xe2x80x94COOxe2x80x94 where O atoms are not directly linked to each other, each of Y31 to Y36 independently represents H or F, or Y33 and Y36 may also be xe2x80x94CH3, each of W31 to W39 independently represents H, F or Cl, each of Z31 to Z36 independently represents a single bond, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2Oxe2x80x94, OCH2xe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Nxe2x95x90CHxe2x80x94 or xe2x80x94N(O)xe2x95x90Nxe2x80x94, wherein each of Z31 and Z34 to Z36 may also be xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, each of the rings A31 to A35 independently represents trans-1,4-cyclohexylene, trans-1,4-cyclohexenylene or trans-1,3-dioxane-2,5-diyl, wherein each of the rings A31 and A33 to A35 may also be 1,4-phenylene, 2- or 3-fluoro-1,4-phenylene, 2,3-difluoro-1,3-phenylene or 3,5-difluoro-1,4-phenylene and, in the case of trans-1,4-cyclohexylene, at least one of the hydrogen atoms in said ring may be replaced by deuterium atom, each of k31 to k35 independently represents 0 or 1 wherein k34+k35 is 0 or 1, and the atoms which constitute the compounds of said general formulae (III-1) to (III-4) may be replaced by their isotopic atoms.
11. The nematic liquid crystal composition described in the aforementioned item 10, wherein said liquid crystal component C contains 1 to 15 compounds selected from the group consisting of the compounds represented by the general formula (III-1), (III-2) or (III-3), and the total content of these compounds in said liquid crystal component C is from 10 to 100% by weight.
12. The nematic liquid crystal composition described in the aforementioned item 10, wherein said liquid crystal component C contains 1 to 15 or more compounds selected from the group consisting of (1) a compound in which each of R31 to R34 in the general formulae (III-1) to (III-4) is independently an alkenyl group having 2 to 5 carbon atoms, (2) a compound in which each of R35 to R38 in the general formulae (III-1) to (III-4) is independently a straight chain alkenyl or alkenyloxy group having 2 to 7 carbon atoms, (3) a compound in which in the general formula (III-1) k31 is 0 and Z32 is a single bond or xe2x80x94(CH2)2xe2x80x94, (4) a compound in which k31 in the general formula (III-1) is 1, (5) a compound represented by the general formula (III-2), (6) a compound in which in the general formula (III-3) at least one of Y34, Y35 and W34 to W36 is F and Y33 is F or xe2x80x94CH3, (7) a compound in which in the general formula (III-3) k33 is 0 and Z36 is a single bond, (8) a compound in which in the general formula (III-3) k33 is 1 and Z35 is a single bond, xe2x80x94OCOxe2x80x94, xe2x80x94CH2Oxe2x80x94, OCH2xe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94N(O)xe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94CFxe2x95x90CFxe2x80x94, (9) a compound in which in the general formula (III-3) Z35 is xe2x80x94COOxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94 and Z36 is xe2x80x94OCOxe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94N(O)xe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, (10) a compound represented by the general formula (III-4), and (11) a compound in which in the general formulae (III-1) to (III-4) the rings A31 to A35 are trans-1,4-cyclohexylene and at least one of the hydrogen atoms in said ring is replaced by deuterium atom.
13. The nematic liquid crystal composition described in the aforementioned item 10, wherein said liquid crystal component C contains 1 to 15 compounds selected from the group consisting of (1) a compound in which in the general formula (III-1) R31 is an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 5 carbon atoms, R35 is an alkyl or alkoxy group having 1 to 5 carbon atoms or an alkenyl or alkenyloxy group having 2 to 5 carbon atoms, k31 is 0 and Z32 is a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94(CH2)2xe2x80x94, (2) a compound in which in the general formula (III-1) k31is 1, the ring A31 is trans-1,4-cyclohexylene and one of Z31 and Z32 is a single bond and the other is xe2x80x94COOxe2x80x94 or xe2x80x94(CH2)2xe2x80x94, (3) a compound in which in the general formula (III-2) R32 is an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 5 carbon atoms, R36 is an alkyl or alkoxy group having 1 to 5 carbon atoms or an alkenyl or alkenyloxy group having 2 to 5 carbon atoms, the ring A32 is trans-1,4-cyclohexylene or trans-1,4-cyclohexenylene, k32 is 0 and Z33 is a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94(CH2)2xe2x80x94, (4) a compound in which in the general formula (III-2) k32 is 1 and one of Z33 and Z34 is a single bond, (5) a compound in which in the general formula (III-3) R33 is an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 5 carbon atoms, R37 is an alkyl or alkoxy group having 1 to 5 carbon atoms or an alkenyl or alkenyloxy group having 2 to 5 carbon atoms, k33 is 0 and Z36 is a single bond, xe2x80x94Cxe2x89xa1Cxe2x80x94 or xe2x80x94CHxe2x95x90Nxe2x80x94Nxe2x95x90CHxe2x80x94, (6) a compound in which in the general formula (III-3) k33 is 1 Z35 is a single bond, xe2x80x94(CH2)2, xe2x80x94COOxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94 and Z36 is a single bond, xe2x80x94COOxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94, (7) a compound in which in the general formula (III-3) one of Z35 and Z36 is a single bond and the other is a single bond or xe2x80x94Cxe2x89xa1Cxe2x80x94 and at least one of W34 and W35 is F, (8) a compound in which in the general formula (III-3) either one of Y35 and Y36 is substituted with F or CH3, and (9) a compound in which in the general formula (III-4) R34 is an alkyl group having 1 to 5 carbon atoms or an alkenyl group having 2 to 5 carbon atoms, R38 is an alkyl or alkoxy group having 1 to 5 carbon atoms or an alkenyl or alkenyloxy group having 2 to 5 carbon atoms and k34+k35 is 0, and wherein the total content of these compounds in said liquid crystal component C is from 10 to 100% by weight.
14. The nematic liquid crystal composition described in any one of the aforementioned items 5 to 13, wherein said liquid crystal composition contains 1 to 10 compounds having a core structure of four six membered rings and having a liquid crystal phase-isotropic liquid phase transition temperature of 100xc2x0 C. or more.
15. The nematic liquid crystal composition described in any one of the aforementioned items 5 to 14, wherein said liquid crystal composition has a birefringence of from 0.08 to 0.195, an elastic constant ratio K33/K11 of from 1.1 to 4.0, a nematic phase-isotropic liquid phase transition temperature of from 50 to 150xc2x0 C. and a crystal phase-, smectic phase- or glass phase-nematic phase transition temperature of from xe2x88x92200xc2x0 C. to 0xc2x0 C.
16. The nematic liquid crystal composition described in any one of the aforementioned items 5 to 15, wherein said liquid crystal composition further contains a compound having an optically active group which shows an induced helical pitch of from 0.5 to 1,000 xcexcm.
17. An active matrix, twisted nematic or super twisted nematic liquid crystal display system comprising the nematic liquid crystal composition described in the aforementioned item 16.